Split electrode for organic devices

ABSTRACT

A device is provided. The device includes a first electrode, an organic layer disposed over the first electrode and a second electrode disposed over the organic layer. The second electrode further includes a first conductive layer having an extinction coefficient and an index of refraction, a first separation layer disposed over the first conductive layer, and a second conductive layer disposed over the first separation layer. The first separation layer has an extinction coefficient that is at least 10% different from the extinction coefficient of the first conductive layer at 500 nm, or an index of refraction that is at least 10% different from the index of refraction of the first conductive layer at 500 nm. The device also includes a barrier layer disposed over the second conductive layer.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to a split electrode.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

A device is provided. The device includes a first electrode, an organiclayer disposed over the first electrode and a second electrode disposedover the organic layer. The second electrode further includes a firstconductive layer having an extinction coefficient and an index ofrefraction, a first separation layer disposed over the first conductivelayer, and a second conductive layer disposed over the first separationlayer. The first separation layer has an extinction coefficient that isat least 10% different from the extinction coefficient of the firstconductive layer at 500 nm, or an index of refraction that is at least10% different from the index of refraction of the first conductive layerat 500 nm. Preferably, the first separation layer has an extinctioncoefficient that is at least 10% different from the extinctioncoefficient of the first conductive layer at 500 nm. More preferably,the first separation layer also has an index of refraction that is atleast 10% different from the index of refraction of the first conductivelayer at 500 nm. The device also includes a barrier layer disposed overthe second conductive layer.

Preferably, the first separation layer has an extinction coefficient at500 nm less than 5, more preferably less than 3, and most preferablyless than 1.

In one embodiment, the first separation layer consists essentially of anorganic material. When the first separation layer is an organicmaterial, the first separation layer preferably has a thickness of atleast 20 nm.

In one embodiment, the first separation layer consists essentially of aninorganic material.

Preferably, the first conductive layer has a thickness not more than 150nm.

Preferably, the first conductive layer has a water vapor transmissionrate at least 5% different from that of the first separation layer, andthe second conductive layer has a water vapor transmission rate at least5% different from that of the first separation layer. More preferably,the first conductive layer has a water vapor transmission rate at least10% different from that of the first separation layer, and the secondconductive layer has a water vapor transmission rate at least 10%different from that of the first separation layer. Most preferably, thefirst conductive layer has a water vapor transmission rate at least 25%different from that of the first separation layer, and the secondconductive layer has a water vapor transmission rate at least 25%different from that of the first separation layer.

In one embodiment, the first conductive layer is a low work functionmetallic layer or an inorganic layer. Preferred low work functionmetallic layer materials for the first conductive layer include Ca andMgAg.

In one embodiment, the second conductive layer is a low work functionmetallic layer or an inorganic layer. Preferred low work functionmetallic layer materials for the second conductive layer include Ca andMgAg.

In one embodiment, the first conductive layer and the second conductivelayer have the same material composition.

In one embodiment, the first conductive layer and the second conductivelayers have different material compositions.

In one embodiment, the first separation layer is a metallic layer, aninorganic layer, or an organic layer.

The device may further comprise a substrate, and the first electrode maybe disposed over the substrate.

In one embodiment, the substrate is a rigid substrate having a flexuralrigidity greater than 2×10⁻² Nm. Preferred materials for a rigidsubstrate include glass, ceramic, and metal having a thicknesssufficient to result in the desired flexural rigidity.

In one embodiment, the substrate is a flexible substrate having aflexural rigidity less than 2×10⁻² Nm. Preferred materials for aflexible substrate include metal, plastic, paper, fabric and a compositematerial. The materials have a thickness sufficiently low to result inthe desired flexural rigidity. Composites can be ceramic matrixcomposites, metal matrix composites, or polymer matrix composites.

In one embodiment, the first electrode is a anode, and the devicefurther includes a permeation barrier layer disposed between the anodeand the substrate. The device also further includes a water reactinglayer disposed between the substrate and the anode. This embodiment isparticularly preferred for use with flexible substrates, which tend tobe more susceptible to moisture penetrating the substrate.

In one embodiment, the device further includes a lamination layerdisposed over the barrier layer. A lamination layer can be a thinpolymer membrane attached to the substrate using an adhesive, a thinspun-on polymer layer, an evaporated polymer layer, a spray coated, oran aerosol dispersed polymer layer.

In one embodiment, the second electrode further includes a secondseparation layer disposed over the second conductive layer, and a thirdconductive layer disposed over the second separation layer. Parametersdescribed above with respect to the second conductive layer and thefirst separation layer are preferred for use with the third conductivelayer and the second separation layer as well.

In one embodiment, the first separation layer consists essentially of asingle material.

In one embodiment, the first separation layer comprises a mixture of atleast two different materials.

In one embodiment, the first separation layer comprises a plurality ofsublayers, wherein at least two of the sublayers have a differentmaterial composition.

Preferably, the barrier layer is transparent.

A method is also provided. The following layers are deposited, in order,over a substrate: a first electrode; an organic layer; a secondelectrode; and a barrier layer. Depositing the second electrode furthercomprises depositing, in order: a first conductive layer having anextinction coefficient and an index of refraction; a first separationlayer disposed over the first conductive layer, and a second conductivelayer disposed over the first separation layer. The first separationlayer has an extinction coefficient that is at least 10% different fromthe extinction coefficient of the first conductive layer at 500 nm.Preferably, the first separation layer also has an index of refractionthat is at least 10% different from the index of refraction of the firstconductive layer at 500 nm.

Embodiments and preferences described above with respect to devices alsoapply to the method.

Embodiments of the invention may be used with a variety of organicdevices. While many embodiments are described herein with respect toorganic light emitting devices, other types of devices, such as organicphotovoltaic devices and organic transistors, may benefit from theelectrode and moisture protective structures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows an organic light emitting device that includes a splitelectrode.

FIG. 4 shows schematic 3-D and cross-sectional views of a device withsingle layer cathode. Formation of dark spots at cathode-organicinterface is also shown.

FIG. 5 shows a schematic 3-D and the cross-sectional views of a devicewith multiple layer cathode. Formation of defects (not forming darkspots) away from the cathode-organic interface is shown.

FIG. 6 shows a cross-sectional view of a flexible device with bottomdesiccant layer and multiple layer cathode. Formation of defects (notforming dark spots) away from the cathode-organic interface above andbelow the device is shown.

FIG. 7 shows a cross-sectional view of a device with multiple layercathode with bridges between the two cathode layers via breaks in thesandwich layer.

FIG. 8 shows a cross-sectional view of a flexible device with multiplelayer cathode with bridges between the two cathode layers via breaks inthe sandwich layer.

FIG. 9 shows a schematic cross-sectional view of organic layer of theOLED device and CL-1 and -2 with a defect separation layer (DSL) inbetween. The DSL has higher water vapor transmission rate than thecathode. This allows the water molecules to disperse across the layerquickly at the same time allowing the CL-2 to react with water and formdefects which are not visible as dark spots in the device.

FIG. 10 shows a schematic cross-sectional view of organic layer of theOLED device and CL-1 and -2 with DSL in between. The DSL has lower watervapor transmission rate than the cathode. This forces the watermolecules to disperse across the interface of the CL-2 with the DSL andreact with the cathode to form defects which are not visible as darkspots in the device.

FIG. 11 shows a schematic cross-sectional view of organic layer of theOLED device and CL-1 and an extended cathode. The pinholes and otherdefects in the cathode continue to grow. The end result is not muchdifferent than if only the first CL were present. The defects form atthe CL-1—organic interface and are visible as dark spots.

FIG. 12 shows photographs of active areas of bottom-emitting OLEDdevices during the shelf-life tests at 85° C. and 85% RH encapsulatedwith similar thin film encapsulation. (a) The cathode is single layer200 nm Al. (b) The cathode is 100 nm Al, followed by 60 nm NPD, followedby 100 nm Al. The lag time (time for the onset of degradation) is about480 hrs in the first case, whereas it is about 650 hrs in the second.

FIG. 13 shows a photographs of active areas of bottom-emitting OLEDdevices during the shelf-life tests at 85° C. and 85% RH encapsulatedwithout thin film encapsulation. (a) and (b) The cathode is single layer200 nm Al. (c) and (d) The cathode is 100 nm Al, followed by 60 nm NPD,followed by 100 nm Al. All the devices got disintegrated by water vaporwithin 10 min at 85° C. and 85% RH.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processability than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, medical monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, vehicles, a large area wall, theater orstadium screen, or a sign. Various control mechanisms may be used tocontrol devices fabricated in accordance with the present invention,including passive matrix and active matrix. Many of the devices areintended for use in a temperature range comfortable to humans, such as18 degrees C. to 30 degrees C., and more preferably at room temperature(20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl; alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

A structure and method to prolong the shelflife of OLEDs encapsulatedwith thin film encapsulation has been discovered. An electrode having aseparation layer disposed between two conductive layers is used todirect the formation of defects caused by insulating film formation orinterface delamination to locations in the device that are away fromcathode-organic interface, such that dark spots are not formed.

A cathode layer (CL) may be divided into two or more conductive layerssandwiching a separation layer between them. Because of this divisionthe water vapor penetrating through the encapsulation layer attacks thetop most conductive or the separation layer of the CL. This oftenresults in a reaction that forms an insulating (oxide-like) layer and/orcauses delamination. Because the water reacts before reaching thebottommost conductive layer of the CL, that layer remains unaffected bythe formation of this defect. As a result, the bottommost conductivelayer of the CL continues functioning as a cathode. In addition, thebottommost conductive layer of the CL undergoing much less degradationwhen compared to a single layer cathode, thereby extending the shelflife of the device.

Another function for the top layer of such a divided cathode is actingas a desiccant to absorb moisture. The function of desiccant can beutilized on the anode side of the device in addition to the cathode sidewhen the substrate is permeable, which is seen most often in the contextof a plastic substrate or a flexible substrate. Plastic substrates arepreferably used with a barrier film between the substrate and the deviceto prevent the device from degrading via the water vapor permeatingthrough the substrate. If there is a thin layer of moisture absorbingmaterial between the cathode and the encapsulation layer, it can reactwith the water molecules, delaying them from reaching thecathode-organic interface and forming dark spots.

There have been attempts to describe the utility of multilayer cathode.E.g., the experiment in the article, “Improved flexibility of flexibleorganic light-emitting devices by using a metal/organic multilayerCathode, by Lian Duan, Song Liu, Deqing Zhang, Juan Qiao, Guifang Dong,Liduo Wang and Yong Qiu, J. Phys. D: Appl. Phys. 42 (2009) 075103”describes improvements in device flexibility and lifetime (operationallifetime, not shelf lifetime) by using a multilayer (Al/Alq/Al) cathodetopped with encapsulation consisting of four stacks of Alq/LiF, followedby CaO desiccant, followed by Al foil.

In contrast to the device disclosed in Duan, the multilayer cathodedescribed herein is suitable for use in a device that emits lightthrough the cathode, and that can be used, for example, in conjunctionwith a barrier layer that is a transparent thin film encapsulation layerdisposed over the cathode.

There have been other attempts to use multilayer cathodes. E.g.US2006/018199A1 demonstrates a metal/inorganic/metal multilayer cathodein an OLED device.

FIG. 3 shows an organic device 300 having a split electrode. The deviceis disposed over a substrate 310. The device includes, in order, apermeation barrier 320, a water reacting layer 330, a first electrode340, an organic layer 350, a second electrode 360, a barrier layer 370,and a lamination layer 380, Second electrode 360 is a split electrodethat further includes a first conductive layer 361, a first separationlayer 362, a second conductive layer 363, a second separation layer 364,and a third conductive layer 365. Many features shown in FIG. 3 areoptional.

A device is provided. The device includes a first electrode, an organiclayer disposed over the first electrode and a second electrode disposedover the organic layer. The second electrode further includes a firstconductive layer having an extinction coefficient and an index ofrefraction, a first separation layer disposed over the first conductivelayer, and a second conductive layer disposed over the first separationlayer. The first separation layer has an extinction coefficient that isat least 10% different from the extinction coefficient of the firstconductive layer at 500 nm, or an index of refraction that is at least10% different from the index of refraction of the first conductive layerat 500 nm. Preferably, the first separation layer has an extinctioncoefficient that is at least 10% different from the extinctioncoefficient of the first conductive layer at 500 nm. More preferably,the first separation layer also has an index of refraction that is atleast 10% different from the index of refraction of the first conductivelayer at 500 nm. The device also includes a barrier layer disposed overthe second conductive layer.

The organic layer may include multiple sublayers. For example, in anOLED, the organic layer may include all or some of the organic layersdescribed with respect to FIGS. 1 and 2. In other types of organicdevices, the organic layer may include multiple layers as well.

By “at least 10% different,” it is meant, for example, that the firstseparation layer has an extinction coefficient that is either 10%greater or 10% less than that of the first conductive layer.

When light passes through a material, the measured intensity I of lighttransmitted through is related to the incident intensity I0 according tothe inverse exponential power law called as Beer-Lambert Law. Theexpression is given by:

I=I ₀ e ⁻

^(x),

where x denotes the path length and

is the absorption or attenuation coefficient. The absorption coefficientis one way to describe the absorption of electromagnetic waves in amedium. It can be expressed in terms of the imaginary part of therefractive index, κ, and the wavelength of the light in free space, λ₀,as

=4πκ/λ₀. The imaginary part of the refractive index is also commonlycalled the extinction coefficient. The extinction coefficient, just likethe real part of the refractive index, has not units. The real part ofthe refractive index (commonly called as the refractive index) of amedium denotes the ratio of the speed of the wave in a reference medium(such as vacuum) to that in the given medium.

A difference in the extinction coefficient and refractive index betweenthe separation layer and other layers is desirable because such adifference means that there is also a difference in material growth,chemistry, composition, density, and atomic arrangement and/or otherphysical properties such as the water vapor transmission rate. It isdesirable to have a separation layer whose material properties aredifferent from that of the conduction layer to perform its function as aseparation layer. A material with different physical properties willallow the water vapor permeating through the permeation barrier getdistributed instead of continuing down to the device in the absence ofsuch layer as shown in FIG. 11. Extinction coefficient and refractiveindex, while correlating to water vapor transmission coefficient, aremore readily obtainable from published references and can be measuredmore easily than water vapor transmission coefficient and hence can beused to pick materials suitable as the separation layer. Extinctioncoefficient or refractive index higher or lower than the conductionlayer would imply difference in the physical properties and hence wouldensure its proper functioning as the separation layer. As an example,the extinction coefficient and the refractive index of a commonly usedconduction layer Al at 500 nm are 6.04 and 0.82. An inorganic film suchas SiON would work well as the separation layer because of thedifference in physical properties between the two materials. It has anextinction coefficient of 0 and a refractive index of 1.49 at 500 nm.From the previous example we see that both extinction coefficient andrefractive index can be used to select a separation layer suitable for aconduction layer. The measurement of these two parameters is very simpleand requires only a few minutes using an ellipsometer

Barrier layers can be inorganic, such as SiNx, SiOx, and SiOxNy, orother oxides such as TiO₂, HfO₂ or nitrides such as TiN or AlTiN, ororganometallic, such as SiOxCy, SiOxCyHz, SiCxOyNz or hybrid (mixturesof) inorganic-organic films, or multiple layers of alternateinorganic-organic films grown using evaporation techniques such aschemical vapor deposition (hot-wire or plasma assisted), or e-beam orthermal evaporation, or sputtering or atomic or molecular layerdeposition. Organic films are compounds containing carbon such as Alq,NPD, polyacrylates, polycarbonates, etc. The barrier films can bedeposited using aforementioned vacuum techniques or non-vacuumtechniques such as printing or spin-on and sintering. Barrier layers areknown, and any suitable barrier layer may be used.

Preferably, the first separation layer has an extinction coefficientless than 5 at 500 nm. More preferably, the first separation layer hasan extinction coefficient less than 3 and even more preferably less than1 at 500 nm

Extinction coefficient and index of refraction are generally functionsof wavelength. 500 nm is selected as a point at which to definitivelyquantify the effects of extinction coefficient and index of refractionbecause higher energy visible light, such as that around 500 nm, maygenerally cause more issues of various types in various devices thanlower energy light.

In one embodiment, the first separation layer consists essentially of anorganic material. When the first separation layer is an organicmaterial, the first separation layer preferably has a thickness of atleast 20 nm.

In one embodiment, the first separation layer consists essentially of aninorganic material.

Preferably, the first conductive layer has a thickness not more than 150nm.

Preferably, the first conductive layer has a water vapor transmissionrate at least 5% different from that of the first separation layer, andthe second conductive layer has a water vapor transmission rate at least5% different from that of the first separation layer. More preferably,the first conductive layer has a water vapor transmission rate at least10% different from that of the first separation layer, and the secondconductive layer has a water vapor transmission rate at least 10%different from that of the first separation layer. Most preferably, thefirst conductive layer has a water vapor transmission rate at least 25%different from that of the first separation layer, and the secondconductive layer has a water vapor transmission rate at least 25%different from that of the first separation layer.

By “at least 5% different,” it is meant, for example, that the firstseparation layer has a water vapor transmission rate (WVTR) that iseither 5% greater or 5% less than that of the first conductive layer. Asignificant difference in the WVTR of these layers means that watertraveling through the electrode somewhere hits a layer with a relativelyhigh WVTR, where it can travel in a direction parallel to the electroderelatively easily and react to form an oxide over a wide area prior toreaching an interface where such a reaction causes a dark spot.

In one embodiment, the first conductive layer is a low work functionmetallic layer or an inorganic layer. Preferred low work functionmetallic layer materials for the first conductive layer include Ca andMgAg (Mg doped with Ag).

In one embodiment, the second conductive layer is a low work functionmetallic layer or an inorganic layer. Preferred low work functionmetallic layer materials for the second conductive layer include Ca andMgAg.

In one embodiment, the first conductive layer and the second conductivelayer have the same material composition.

In one embodiment, the first conductive layer and the second conductivelayers have different material compositions.

In one embodiment, the first separation layer is a metallic layer, aninorganic layer, or an organic layer.

The device may further comprise a substrate, and the first electrode maybe disposed over the substrate.

In one embodiment, the substrate is a rigid substrate having a flexuralrigidity greater than 2×10⁻² Nm. Preferred materials for a rigidsubstrate include glass, ceramic, and metal having a thicknesssufficient to result in the desired flexural rigidity.

In one embodiment, the substrate is a flexible substrate having aflexural rigidity less than 2×10⁻² Nm. Preferred materials for aflexible substrate include metal, plastic, paper, fabric and a compositematerial. The materials have a thickness sufficiently low to result inthe desired flexural rigidity. Composites can be ceramic matrixcomposites, metal matrix composites, or polymer matrix composites.

In one embodiment, the first electrode is a anode, and the devicefurther includes a permeation barrier layer disposed between the anodeand the substrate. The device also further includes a water reactinglayer disposed between the substrate and the anode. This embodiment isparticularly preferred for use with flexible substrates, which tend tobe more susceptible to moisture penetrating the substrate.

The permeation barrier can be anywhere from 100 nm thick film in a lowdefect, low particulate scenario to a 50 μm thick film such as acombination of some thin inorganic film (like SiOxCyNz) with spun-on orevaporated or printed polymer film (like polyacrylate or polyepoxide).Preferably, the overall barrier layer is less than 25 μm thick and mostpreferably less than 10 μm thick. Reducing the thickness would improvethe mechanical flexibility of the barrier film. The water reacting layercan be as thin as 5 nm when it is a thin metal film or as thick as 25 μmwhen it is a polymer film. The water reactive film, when it is polymer,can also act as a planarization layer used to minimize the surfaceroughness of the substrate.

In one embodiment, the device further includes a lamination layerdisposed over the barrier layer. Its purpose is to prevent the barrierlayer from mechanical degradation upon handling and transport. Alamination layer can be a thin polymer membrane attached to thesubstrate using an adhesive, a thin spun-on polymer layer, an evaporatedpolymer layer, a spray coated, or an aerosol dispersed polymer layer.

The lamination layer can be a layer of an organic or organometalliccompound such as polyacrylates, polyepoxides, polysiloxanes, and othersuitable materials. These can be UV or heat curable compounds, whichwill polymerize, or cross-link or set upon treating with UV light orheating or applying pressure, or simply leaving at room temperature forsome interval of time. The lamination can also be such polymer adhesivelayers followed by a polymer membrane or sheet such as PEN (polyethylenenepthlate), or polycarbonate, or polyimide or other suitable materials.

In one embodiment, the second electrode further includes a secondseparation layer disposed over the second conductive layer, and a thirdconductive layer disposed over the second separation layer. Parametersdescribed above with respect to the second conductive layer and thefirst separation layer are preferred for use with the third conductivelayer and the second separation layer as well.

An additional separation layer increases the number of interfaces andlayers in which water can travel laterally and react prior to reachingan interface with the organic material, where the presence of waterwould cause a dark spot.

In one embodiment, the first separation layer consists essentially of asingle material.

In one embodiment, the first separation layer comprises a mixture of atleast two different materials.

In one embodiment, the first separation layer comprises a plurality ofsublayers, wherein at least two of the sublayers have a differentmaterial composition.

Preferably, the barrier layer is transparent. As used herein,“transparent” means that the layer transmits more than 90% of incidentlight having a wavelength of 500 nm.

A method is also provided. The following layers are deposited, in order,over a substrate: a first electrode; an organic layer; a secondelectrode; and a barrier layer. Depositing the second electrode furthercomprises depositing, in order: a first conductive layer having anextinction coefficient and an index of refraction; a first separationlayer disposed over the first conductive layer, and a second conductivelayer disposed over the first separation layer. The first separationlayer has an extinction coefficient that is at least 10% different fromthe extinction coefficient of the first conductive layer at 500 nm.Preferably, the first separation layer also has an index of refractionthat is at least 10% different from the index of refraction of the firstconductive layer at 500 nm.

Embodiments and preferences described above with respect to devices alsoapply to the method.

Embodiments of the invention may be used with a variety of organicdevices. While many embodiments are described herein with respect toorganic light emitting devices, other types of devices, such as organicphotovoltaic devices and organic transistors, may benefit from theelectrode and moisture protective structures described herein.

FIG. 4 shows schematic 3-D and cross-sectional views of a device withsingle layer cathode. Formation of dark spots at cathode-organicinterface is also shown. The device of FIG. 4 includes a substrate 410,an anode 420, organic layers 430, a cathode 440 and a barrier film 450.A bus line 460 provides current to the cathode. Dark spot 470 is alsoshown.

Embodiment 1

In one embodiment, a moisture sensitive electrode of an electronicdevice is divided in to two or more layers with another metallic,inorganic or organic layer sandwiched in between to mitigatedegradation. By way of comparative example, FIG. 4 shows the 3-D and thecross-sectional views (both schematic) of a device with single layercathode. The dark spots form when water vapor penetrates through theencapsulation film to reach the cathode-organic interface, causingaffected regions to stop emitting.

FIG. 5 shows a schematic 3-D and the cross-sectional views of a devicewith a multiple layer or “split” cathode. Formation of defects (notforming dark spots) away from the cathode-organic interface is shown.The device of FIG. 5 includes a substrate 510, an anode 520, organiclayers 530, a cathode, and a barrier film 550. The cathode includesfirst conductive layer 541, separation layer 542 and second conductivelayer 543. Dark spot 460 is also shown.

In FIG. 5, which shows the 3-D and the cross-sectional views of a devicewith split-cathode, the delamination defects form at the interfacebetween the second conductive layer and the separation layer. As thedefects are away from the active area, the device continues to emitlight. The defect separation layer (DSL) has a different water vaporpermeation rate than the cathode. In one case, it has much higher watervapor permeation rate than the cathode. The high permeation rate resultsin quick dispersion of water molecules across the sandwich layer andallows sufficient time for the second conductive layer (cathode layer 2or CL-2)—DSL interface to react with the moisture. Note that the firstconductive layer may also be referred to as cathode layer 1 or CL-1. Inanother case, the permeation rate across the sandwich layer is much lessthan the cathode. In that case, the water vapor will be forced to travelacross the interface of the CL-2—DSL interface allowing it to react withthe cathode.

Embodiment 2

FIG. 6 shows a cross-sectional view of a flexible device with bottomdesiccant layer and multiple layer cathode. Formation of defects (notforming dark spots) away from the cathode-organic interface is shown.The device of FIG. 6 includes a substrate 610, a permeation barrierlayer 611 (also called a bottom barrier layer), a water reacting layer612 (also called a bottom dessicant layer), bottom an anode 620, organiclayers 630, a cathode, and a barrier film 650. The cathode includesfirst conductive layer 641, separation layer 642 and second conductivelayer 643. Dark spot 660 is also shown.

The embodiment of FIG. 6 involves a flexible substrate which ispermeable to water vapor. Such a substrate preferably involves the useof a bottom barrier film. In such a device water vapor travels from bothtop and bottom sides. As in previous embodiment, water vapor coming fromboth top and bottom sides may reach the water sensitive cathode and formdefects at the cathode-organic interface which would appear as darkspots in the device. In addition to the split-cathode, this embodimenthas thin moisture reacting layer sandwiched between the bottom barrierand the anode. This layer acts as a desiccant layer absorbing the watermolecules coming through the plastic substrate and the bottom barrierlayer.

Embodiment 3

FIG. 7 shows a cross-sectional view of a device with multiple layercathode with bridges between the two cathode layers via breaks in thesandwich layer. Formation of defects (not forming dark spots) away fromthe cathode-organic interface is shown. The device of FIG. 7 includes asubstrate 710, a first electrode 720, organic layers 730, a secondelectrode, and a barrier film 750. The cathode includes first conductivelayer 741, separation layer 742 and second conductive layer 743. Darkspot 760 is also shown.

In the embodiment of FIG. 7, the first and second conductive layers arebridged by bridges 744. That is, separation layer 742 has regions whereit allows the first and second conductive layers to touch. Separationlayer 742 is not necessarily continuous. This configuration utilizes theconductivity of the second conductive layer. Over a period of storage,because of defect formation, the second conductive layer may becomecompletely electrically isolated from the underlying device. For a thincathode, this would mean that only the first conductive layer wouldparticipate in carrier transport. A very thin cathode would have highresistance which can make the device non-uniform when operated. If thesecond (and possibly any additional) conductive layers are bridged tothe first conductive layer, the combined stack would still have an inputin the overall conduction. Because the bridges occupy only a fraction ofthe area of the second electrode, they do not have as deleterious aneffect on the formation of dark spots as a simple single layerelectrode. FIGS. 7 and 8 illustrate this embodiment for rigid andflexible substrates, where FIG. 8 adds to FIG. 7 a permeation barrierlayer 711 (also called a bottom barrier layer), a water reacting layer712 (also called a bottom dessicant layer).

FIG. 9 shows a schematic cross-sectional view of organic layer of theOLED device and CL-1 and -2 with a defect separation layer (DSL) inbetween. The DSL has higher water vapor transmission rate than thecathode. This allows the water molecules to disperse across the layerquickly at the same time allowing the CL-2 to react with water and formdefects which are not visible as dark spots in the device.

FIG. 10 shows a schematic cross-sectional view of organic layer of theOLED device and CL-1 and -2 with DSL in between. The DSL has lower watervapor transmission rate than the cathode. This forces the watermolecules to disperse across the interface of the CL-2 with the DSL andreact with the cathode to form defects which are not visible as darkspots in the device.

FIG. 11 shows a schematic cross-sectional view of organic layer of theOLED device and CL-1 and an extended cathode. The pinholes and otherdefects in the cathode continue to grow. The end result is not muchdifferent than if only the first CL were present. The defects form atthe CL-1—organic interface and are visible as dark spots.

Method of Device Fabrication

The device fabrication method can be divided into the following steps:

1. Substrate, planarization*, and bottom permeation barrier*2. Bottom desiccant*(only for flexible permeable substrate)

3. OLED Deposition 4. Cathode Deposition 5. Thin Film Encapsulation 6.Lamination

The use of a planarization layer and a bottom permeation barrier arepreferred only for use with flexible substrates, which tend to havesignificant water permeability. Rigid substrates can generally be madethick enough that water permeation through the substrate is not anissue, although there may be exceptions.

1. Substrate, planarization, and bottom permeation barrier: Rigidsubstrates could be any glass, or ceramic, or thick metallic substrate.Flexible substrates could be thin metal foils, such as Al or stainlesssteel, or plastics, such as PET or PEN, or paper or fabric or compositessuch as ceramic matrix composites, metal matrix composites, or polymermatrix composites. Substrates could comprise a single material, compoundmaterials and/or laminated layers.

Flexible substrates are preferably planarized prior to OLED growth.Flexible metal and plastic substrates often suffer from high asperitycount and high rms roughness. Various planarization methods can be used,such as deposition of a resist (e.g. polyimide), followed by a hardbake, or alternatively deposition of an inorganic dielectric usingmethods such as PECVD. The planarization layer may remove electricalcontact between the OLED and the substrate. This is particularlydesirable in the case of metal foils, where in some circumstances it maybe advantageous not to have electrical current flowing through thesubstrate. The planarization layer may also act as a permeation barrier,which is particularly desirable in the case of plastic substrates, whereoxygen and moisture can permeate through the substrate.

2. Bottom desiccant: For permeable substrates, it is preferred todeposit a thin film layer after the barrier layer that is a moistureconsuming or water reacting layer. It can be any metal, or inorganic, ororganic material or combinations thereof which can form a chemicalcompound with water.

3. OLED Deposition: The anode and/or bus lines could be deposited by anysuitable technique, including VTE or sputtering through a shadow mask,or blanket deposited and then patterned using photolithography. Examplesof anode materials include IZO, ITO, Al, Ag or combinations thereof.Individual anode areas are preferably patterned around the cuts/scoresin the substrate.

Examples of bus line materials include Al, Ag, Au, Cu. Bus lines maypass over score marks made on the reverse of the substrate. In someexamples individual pixel areas are connected in parallel using buslines, whereas in other examples pixels are connected in series. In someexamples, a single large area pixel could be used.

4. Cathode Deposition: The layer on top of the OLED stack is the CL(cathode layer). The split-CL for both rigid and flexible substrates is,as described before, a stacked cathode in which the first layer is actsas a conduction and electron injection layer, whereas the remaininglayers act to move dark spot forming defects away from thecathode-organic interface. The first CL be any suitable low workfunction layer such as Ca or MgAg, deposited by evaporation or otherthin film deposition processes. The DSL can be any thin metallic,organic, or inorganic layer whose function is to separate the comingsecond CL from the first CL. The DSL must be different from the cathodein terms of water vapor transmission. It should either have higherpermeation rate than the cathode so that water molecules upon reachingthe DSL get dispersed quickly at the interface allowing them to formdefects at the interface itself. FIG. 6 describes this situation. Or itshould have lower permeation rate that the cathode so that watermolecules are forced to follow the interface path, react with cathodeand form defects. FIG. 7 describes this situation. In both the cases thedefects form away from the cathode-organic interface which is whatintended. The DSL cannot be an extended (thicker) cathode. In such acase, the water vapor would travel unintruded to the cathode-organicinterface. FIG. 8 describes this situation. The sandwich layer itselfcan absorb moisture. The second CL can be another low work functionmetal or inorganic film like the first cathode. It can be different fromthe first cathode. In some cases more than two cathode layers can beused to enhance the defect separation and moisture consumption effect.In some cases the top most CL can be topped by another organic orinorganic layer to prevent the cathode from getting damaged by theencapsulation process to follow.

5. Thin Film Encapsulation (TFE): When fabricating an OLED on a flexiblesubstrate, especially, but many times on rigid substrates also, thinfilm encapsulation (TFE) is used to prolong the shelflife of device.Thin film encapsulation layers can be inorganic or a combination ofinorganic and organic materials. The inorganic materials provide aneffective barrier against the permeation of moisture and oxygen, whilethe organic materials provide mechanical flexibility and help todistribute any faults in the inorganic layers, which increase thediffusion path length through the barrier.

In the first embodiment descried above we used PECVD to deposit a TFElayer of thickness <10 microns through the shadow mask design.

6. Lamination: For all devices with TFE, the top layer after theencapsulation is the lamination layer. If can consist of a thin polymermembrane attached to the substrate using an adhesive, or a thin spun-onpolymer layer, or an evaporated polymer layer, or a spray coated,aerosol dispersed polymer layer. The lamination layer prevents the thinfilm encapsulation from getting scratched or damaged during handling. Itcan also perform optical function when desired. In the flutteringlighting device embodiment, the lamination layer is an aerosol dispersedpolymer film on top of the thin film encapsulation.

While the method above is described with respect to a device having acathode as the second electrode, it is understood that embodiments mayalso involve an anode used as the second electrode, i.e., the electrodefurther away from the substrate.

Example 1

Some of the inventive concepts were tested by preparing bottom-emittingOLED (BOLED) devices and encapsulating them with thin filmencapsulation. The first device had 200 nm thick Al cathode and thesecond had 100 nm Al, 60 nm NPD, and 100 nm Al cathode. The devices wereencapsulated with similar thin film (same thickness) encapsulationbarrier films and then were stored at 85° C. and 85% RH for shelf-lifetests. FIG. 12 shows the photographs of active areas of the devicesduring the shelf-life tests. Using the single layer cathode (left side),the maximum lag time (i.e., the time until noticeable device degradationoccurs) obtained was around 500 hrs. Using the bifurcated cathode (rightside), the lag time increased to about 650 hrs. Under the acceleratedconditions of 85° C. and 85% RH this is a 30% increase in the lag time.

A comparison was also made of the devices discussed with respect to FIG.12 to similar devices without thin film encapsulation. FIG. 13 showsphotographs of active areas of bottom-emitting OLED devices during theshelf-life tests at 85° C. and 85% RH encapsulated with and without thinfilm encapsulation, and with and without a split cathode. (a) showsphotographs for a single layer 200 nm Al cathode, without encapsulation(b) shows photographs for a single layer 200 nm Al cathode, withencapsulation. (c) shows photographs for a cathode that is 100 nm Al,followed by 60 nm NPD, followed by 100 nm Al, without encapsulation. (d)shows photographs for devices similar to those of (c), but withencapsulation. The devices with and without the defect separation layerlasted only 10 min in such harsh atmospheric conditions, but the deviceswith a defect separation layer performed lasted noticeably longer.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but not limit to: aphthalocyanine or porphryin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and silane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, azulene; group consisting aromaticheterocyclic compounds such as dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine; and groupconsisting 2 to 10 cyclic structural units which are groups of the sametype or different types selected from the aromatic hydrocarbon cyclicgroup and the aromatic heterocyclic group and are bonded to each otherdirectly or via at least one of oxygen atom, nitrogen atom, sulfur atom,silicon atom, phosphorus atom, boron atom, chain structural unit and thealiphatic cyclic group. Wherein each Ar is further substituted by asubstituent selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

k is an integer from 1 to 20; X¹ to X⁸ is C (including CH) or N; Ar¹ hasthe same group defined above.

Examples of metal complexes used in HIL or HTL include, but not limit tothe following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹-Y²) is abidentate ligand, Y¹ and Y² are independently selected from C, N, O, P,and S; L is an ancillary ligand; m is an integer value from 1 to themaximum number of ligands that may be attached to the metal; and m+n isthe maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹-Y²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹-Y²) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidationpotential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant. While the Table below categorizes host materials as preferredfor devices that emit various colors, any host material may be used withany dopant so long as the triplet criteria is satisfied.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

M is a metal; (Y³-Y⁴) is a bidentate ligand, Y³ and Y⁴ are independentlyselected from C, N, O, P, and S; L is an ancillary ligand; m is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and m+n is the maximum number of ligands that maybe attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y³-Y⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the groupconsisting aromatic hydrocarbon cyclic compounds such as benzene,biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene,phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; groupconsisting aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and group consisting 2 to 10 cyclic structural units which are groups ofthe same type or different types selected from the aromatic hydrocarboncyclic group and the aromatic heterocyclic group and are bonded to eachother directly or via at least one of oxygen atom, nitrogen atom, sulfuratom, silicon atom, phosphorus atom, boron atom, chain structural unitand the aliphatic cyclic group. Wherein each group is furthersubstituted by a substituent selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof.

In one aspect, host compound contains at least one of the followinggroups in the molecule:

R¹ to R⁷ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof, when it is aryl or heteroaryl, it has the similardefinition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from C (including CH) or N.

Z¹ and Z² is selected from NR¹, O, or S.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, compound used in HBL contains the same molecule or thesame functional groups used as host described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integerfrom 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

R¹ is selected from the group consisting of hydrogen, deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof, when it is arylor heteroaryl, it has the similar definition as Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from C (including CH) or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atomsO, N or N, N; L is an ancillary ligand; m is an integer value from 1 tothe maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of the OLED device,the hydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. A device, comprising: a first electrode; an organic layer disposedover the first electrode, and; a second electrode disposed over theorganic layer, the second electrode further comprising, a firstconductive layer having an extinction coefficient and an index ofrefraction; a first separation layer disposed over the first conductivelayer, the first separation layer having an extinction coefficient thatis at least 10% different from the extinction coefficient of the firstconductive layer at 500 nm; or wherein the first separation layer has anindex of refraction that is at least 10% different from the index ofrefraction of the first conductive layer at 500 nm; a second conductivelayer disposed over the first separation layer; and a barrier layerdisposed over the second conductive layer.
 2. The device of claim 1,wherein the first separation layer has an extinction coefficient that isat least 10% different from the extinction coefficient of the firstconductive layer at 500 nm.
 3. The device of claim 2, wherein the firstseparation layer has an extinction coefficient less than 5 at 500 nm. 4.The device of claim 2 wherein the first separation layer has anextinction coefficient less than 3 at 500 nm.
 5. The device of claim 2,wherein the first separation layer has an extinction coefficient lessthan 1 at 500 nm.
 6. The device of claim 1, wherein the first separationlayer consists essentially of an organic material.
 7. The device ofclaim 6, wherein the first separation layer has a thickness of at least20 nm.
 8. The device of claim 1, wherein the first separation layerconsists essentially of an inorganic material.
 9. The device of claim 1,wherein the first conductive layer has a thickness not more than 150 nm.10. The device of claim 1, wherein the first conductive layer has awater vapor transmission rate at least 5% different from that of thefirst separation layer, and the second conductive layer has a watervapor transmission rate at least 5% different from that of the firstseparation layer.
 11. The device of claim 1, wherein the firstconductive layer has a water vapor transmission rate at least 10%different from that of the first separation layer, and the secondconductive layer has a water vapor transmission rate at least 10%different from that of the first separation layer.
 12. The device ofclaim 1, wherein the first conductive layer has a water vaportransmission rate at least 25% different from that of the firstseparation layer, and the second conductive layer has a water vaportransmission rate at least 25% different from that of the firstseparation layer.
 13. The device of claim 1, wherein the firstconductive layer is a low work function metallic layer or an inorganiclayer.
 14. The device of claim 13, wherein the first conductive layer isa low work function metallic layer comprising a material selected fromAl, Ca and MgAg.
 15. The device of claim 1, wherein the secondconductive layer is a low work function metallic layer or an inorganiclayer.
 16. The device of claim 15, wherein the second conductive layeris a low work function metallic layer comprising a material selectedfrom Al, Ca, and MgAg.
 17. The device of claim 1, wherein the firstconductive layer and the second conductive layer have the same materialcomposition.
 18. The device of claim 1, wherein the first conductivelayer and the second conductive layers have different materialcompositions.
 19. The device of claim 1, wherein the first separationlayer is a metallic layer, an inorganic layer, or an organic layer. 20.The device of claim 1, wherein the device further comprises a substrate,and the first electrode is disposed over the substrate.
 21. The deviceof claim 20, wherein the substrate is a rigid substrate having aflexural rigidity greater than 2×10⁻² Nm.
 22. The device of claim 21,wherein the substrate is a flexible substrate having a flexural rigidityless than 2×10⁻² Nm.
 23. The device of claim 22, wherein the firstelectrode is a anode, and the device further comprises: a permeationbarrier layer disposed between the anode and the substrate; and a waterreacting layer disposed between the substrate and the anode.
 24. Thedevice of claim 20, further comprising a lamination layer disposed overthe barrier layer.
 25. The device of claim 1, wherein the secondelectrode further comprises: a second separation layer disposed over thesecond conductive layer, and a third conductive layer disposed over thesecond separation layer.
 26. The device of claim 1, wherein the firstseparation layer consists essentially of a single material.
 27. Thedevice of claim 1, wherein the first separation layer comprises amixture of at least two different materials.
 28. The device of claim 1,wherein the first separation layer comprises a plurality of sublayers,wherein at least two of the sublayers have a different materialcomposition.
 29. The device of claim 1, wherein the barrier layer istransparent.
 30. A method, comprising: depositing over a substrate: afirst electrode; an organic layer; a second electrode; and a barrierlayer; wherein depositing the second electrode further comprisesdepositing, in order, a first conductive layer having an extinctioncoefficient and an index of refraction; a first separation layerdisposed over the first conductive layer, the first separation layerhaving an extinction coefficient that is at least 10% different from theextinction coefficient of the first conductive layer at 500 nm; a secondconductive layer disposed over the first separation layer.